Danger High Voltage

DANGER HIGH VOLTAGE!

NEVER OPEN THE CASE OF ANY VIDEO MONITOR, UNLESS YOU REALLY KNOW WHAT YOU ARE DOING,

YOU MUST KNOW EXACTLY WHAT YOU ARE DOING TO HANDLE A CRT SAFELY.

Some common procedures for working on electronic equipment include.

Unplug Equipment being worked on. At times you will need to power up the monitor when testing and taking voltage reading, Before attempting to replace any parts capacitors – IC or Diodes insure all Voltage is removed from the monitor.

Allow capacitors to discharge before opening unit.

Discharge CRT tubes to prevent shock.

CRT tubes present an implosion hazard, handle with care.

Always wear eye protection.

Keep hands out of powered units

To work safely on a CRT, you need to set up a CRT-safe electrical area and follow these safety rules every time.

1)       Don't work alone. It could save your life if someone is nearby in case of an accident

2)       Turn off the power and disconnect the AC power cord before you remove the CRT cover.

3)       Remove any metal jewelry

4)       Remove the grounding wrist strap or heel strap

5)       Disconnect the snap fastener on the grounded workbench mat

6)       Wear safety goggles.

7)       Discharge the CRT immediately after the case has been removed and before touching anything inside the monitor

8)       Putting one hand in your pocket or behind your back helps to prevent current from passing through your heart if you touch a high-voltage area.

It is essential - for your safety and to prevent damage to the device under test as well as your test equipment - that large or high voltage capacitors be fully discharged before soldering is attempted, or the circuitry is touched in any way.

This doesn't mean that every one of the many capacitors in your Monitor need to be discharged every time you power off and want to make a measurement. However, the large main filter capacitors and other capacitors in the power supplies should be checked and Discharged if any significant voltage is found after powering off (or before any testing - some capacitors (like the high voltage of the CRT in a video monitor) will retain a dangerous or at least painful charge for days or longer!)

TO DISCHARGE THE CRT

The Bench Tech shop, we have a ground wire from the wall AC outlet box running up to the side of the bench.

Attach the Alligator clip from the High Voltage Probe to the Green Ground Wire

The Best tool for Discharging CRT is the High Voltage Probe

Using this tool, you can watch the Voltage drop to Zero (0), Also you can use it to test the High Voltage – while you have the monitor on..

Note: If you do not have a discharge tool, you can use an insulated screwdriver attached to a wire lead with alligator clips on both ends as shown in the following photos & graphic.

This is my tool, I use it just about daily.

Obviously, make sure that you are well insulated!

Important: If a discharged CRT must remain exposed for any length of time, establish an ongoing lead between the anode and ground.

Warning: To ensure your safety and protection, it is important that you do not touch any of the following parts inside the Monitor housing.

Yoke assembly

Yoke cable/connector

High voltage cable

Anode connector

Fly backt the primary fuse

Any soldered connections

Exposed uninsulated wires

Warning: If you crack a CRT, it can implode, resulting in glass fragments as air rushes into the tube. To avoid cracking a CRT, you must:

Use extreme caution when working around the neck of the CRT

Never handle a CRT by the neck when you remove or replace it.

Disposing of dead monitors (CRTs, here is my recommendation)

Treat the CRT with respect - the implosion hazard should not be minimized.

A large CRT will have over 10 tons of air pressure attempting to crush it.

Wear eye protection whenever dealing with the CRT. 

Handle the CRT by the Front - not the neck or thin funnel shaped envelope. 

Don't just toss it in the garbage - it is a significant hazard.  The vacuum can be safely released (Let out?  Sucked in?)

Without spectacular effects by breaking the glass seal in the center of the CRT socket (may be hidden by the indexing plastic of the socket). 

Cover the entire CRT when doing this for additional protection.

Once the vacuum is gone, it is just a big glass bottle though there may be

Some moderately hazardous materials in the phosphor coatings and of course,

The glass and shadow mask will have many sharp edges if it is broken.

We have a procedure for disposing of used CRT’s. The vacuum must be broken to

Avoid future implosion, like when it will be crushed by the dumpster press.

Another method is to punch or drill a small hole in the anode contact, which is made of a soft metal. But take care of the electrical discharge first!!!

I would also like to add two (2) other things in this. As I have more fear of the Flyback then I do from discharging the CRT

1)     Do not Test or turn on power to any monitor that is on a cart with wheels. It’s would be a normal response to hold onto the monitor as you plug it in to prevent the monitor from rolling away. The Problem would be if the Monitors Flyback were cracked and shorting to the Case. Where is your hand?

2) Clean off the Flyback and inspect it for cracks or holes before trying to adjust the Voltage and or Focus. If it’s cracked or has a hole you will be shocked. I would think it would be more then what the CRT would hold.

You will be surprised what you could find under the dirt

This was a very small hole –

The Spark that came out wasn't and  it HURT